This book is the result of more than five years of intensive research in collaborationwith a large number of people. Since the beginning, our goal has been to understand at a deeper level how information-theoretic security ideas can help build more secure networks and communication systems. Back in 2008, the actual plan was to finish the manuscript within one year, which for some reason seemed a fairly reasonable proposition at that time. Needless to say, we were thoroughly mistaken. The pace at which physical-layer security topics have found their way into the main journals and conferences in communications and information theory is simply staggering. In fact, there is now a vibrant scientific community uncovering the benefits of looking at the physical layer from a security point of view and producing new results every day. Writing a book on physical-layer security thus felt like shooting at not one but multiple moving targets.

To preserve our sanity we decided to go back to basics and focus on how to bridge the gap between theory and practice. It did not take long to realize that the book would have to appeal simultaneously to information theorists, cryptographers, and network-security specialists. More precisely, the material could and should provide a common ground for fruitful interactions between those who speak the language of security and those who for a very long time focused mostly on the challenges of communicating over noisy channels.